The world has changed since Mordechai Vanunu was jailed 18 years ago, not least in the field of Israel's nuclear weaponry on which he had blown the whistle. The Israeli armed forces now possess missiles capable of delivering a nuclear payload up to 1,500 kilometres away, and are developing others with much longer range. They have acquired more than 200 nuclear-capable aircraft, and have completed the land-air-and-sea triad by buying three nuclear-capable submarines. They probably have more nuclear warheads than Britain, including thermonuclear warheads.

Israel is a fully-fledged member of the nuclear club and possessor of weapons of mass destruction, with just one difference - that it will not admit to the fact. Nor will its U.S. ally: Israel is never listed by Washington's intelligence agencies among the countries which have acquired W.M.D. In 1970 President Nixon agreed with Prime Minister Golda Meir that if Israel kept its weapons 'in the basement,' the U.S. would not press it. In 1998 President Clinton went further, with a pledge to support the enhancement of Israel's 'deterrent capabilities' - a euphemism for nuclear weapons.

Other Western governments also steer clear of the subject: Israel still maintains its 'nuclear ambiguity.' Yet today is a rare opportunity, in the publicity surrounding Mr. Vanunu's release, to take stock of this perverse silence. Whatever may have been argued in the past, the world now demands - and no one is more vociferous on the subject than the U.S. - full transparency from those who may possess W.M.D. A war has just been fought with that avowed purpose in Iraq. At a time when Iran and Libya have been encouraged to take the open road, why should Israel be exempt? Any prospect of serious steps against nuclear proliferation, such as persuading the new nuclear powers (India and Pakistan as well as Israel) to accept international restraints, or working towards a nuclear-free zone in the Middle East - which Britain says it supports - is stymied as long as the Israeli bomb remains in the basement.

As for Mr. Vanunu, we should deplore the inhumane way in which he was treated in prison where he spent two-thirds of his time in solitary confinement, the leaking of material designed to alienate any public sympathy in Israel for him and the restrictions now placed on his freedom. He may be a traitor to the Israeli state, as Shimon Peres, architect of the nuclear programme, called him yesterday, but in exposing a secret which needed to be told he has shown a higher duty to wider humanity.